1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor, and specifically to an electrophotographic photoreceptor used in an image forming apparatus to which electrophotographic method applies.
2. Description of Related Art
In recent years, organic photoreceptors including organic photo conductive materials are widely used as electrophotographic photoreceptors. Organic photoreceptors have advantages that they are easy to develop materials corresponding to various types of lithography light sources including visible light to ultra violet light, that materials which do not cause environmental pollution can be selected to be used and that manufacturing cost is inexpensive comparing to inorganic photoreceptors.
On the other hand, because electrophotographic photoreceptors (hereinafter, also called a photoreceptor) directly receives electrical or mechanical external force due to electrification, exposure, development, transfer, cleaning and the like, it is expected that electrophotographic photoreceptors have durability so as to stably maintain electrification stability, electric potential retentivity and such like even when image forming is repeatedly performed.
Especially, with the trend of digitalization in the recent years, demand for high definition and high quality image, is increasing and small particle toners of polymerization method such as a solution suspension toner, emulsion aggregation toner and the like became the mainstream. Such small particle toner has great adhesion on the surface of a photoreceptor and residual toner such as residual toner from transfer attached to the surface of the photoreceptor cannot be removed sufficiently. In a cleaning method using a rubber blade, phenomenon such as “slip through of toner” where toner slips through the blade, “blade turning” where the blade turns over, so-called “blade squeaking” where the photoreceptor and the blade generate friction sound and the like are likely to occur. The blade needs to have great contacting pressure with respect to the photoreceptor in order to resolve the “slip through of toner”. However, there is a problem that the durability becomes insufficient due to attrition of the surface of the organic photoreceptor by repeatedly using the photoreceptor. Further, photoreceptor is expected to have sufficient durability with respect, to degradation due to ozone and nitrogen oxide which are generated at the time of electrification.
In view of the above problems, there is suggested a technique to improve the mechanical strength of photoreceptors by providing protective layer (hereinafter, also called surface layer) on the surfaces of photoreceptors.
In particular, JP H11-288121 and JP 2009-69241 suggest techniques to manufacture a photoreceptor having high durability with respect to attrition and scars on the surface due to friction of a cleaning blade or the like by using a polymerizable compound generally called curable compound as the photoreceptor protective layer and by causing hardening reaction after applying such, polymerizable compound. Further, JP 2002-333733 suggests a technique to improve mechanical strength by dispersing inorganic fine particles such as silica on the protective layer.
In recent years, electrophotographic image forming apparatus has been rapidly expanding its use in the field of light printing, and greater durability and higher image quality is being demanded in electrophotographic photoreceptor. However, electrophotographic photoreceptor that fully satisfies the demand in terms of durability and image quality cannot be obtained in conventional techniques, and there has been increasing demands for techniques which will provide greater durability and higher image quality in electrophotographic photoreceptor.
However, because charge transport ability of such protective layer is poor, there is a problem that the photographic sensitivity characteristic as electrophotographic photoreceptor is to be degraded by being provided with the protective layer comparing to an electrophotographic photoreceptor without protective layer. In order to resolve this problem, the protective layer can have charge transport ability by including charge transport material in the protective layer. However, because, charge transport material of organic compound generally has a plasticizing effect, strength of the protective layer is degraded due to inclusion of charge transport material. In view of the above, there is disclosed a technique to give charge transport ability to the protective layer and to obtain a protective layer having great durability to attrition. For example, JP 2010-164646 discloses a technique regarding a protective layer made by using a radical polymerizable compound having charge transport ability, a radical polymerizable compound not having charge transport ability and a filler which is treated with a surface processing agent including polymerizable functional group and by causing hardening reaction thereof.